1. Field of the Invention
The present invention relates to a brushless motor having therein a chucking mechanism allowing an optical disk to be detachably placed thereon, and to a disk driving device having therein the brushless motor.
2. Description of the Related Art
In recent years, due to a very high speed rotation of an optical disk such as CDs and DVDs, when a mechanism for rotating the disk has a balance problem, the disk may vibrate severely. The vibration may cause a problem when recording data on the disk or reproducing data from the disk. Therefore, a brushless motor having a balance correction feature has been developed.
FIG. 7 indicates a conventional brushless motor 1 having the balance correction feature. According to FIG. 7, the brushless motor 1 includes a shaft 2a which rotates along the central axis J1, a rotor portion 2 having therein a rotor holder 2b of a substantially cylindrical shape affixed to the shaft 2a and a rotor magnet 2c affixed to an inner circumferential surface of a cylindrical portion 2b1 of the rotor holder 2b, a stator portion 3 including a stator 3a arranged opposing in a radial direction to the rotor magnet 2c and a bearing portion 3b affixed to an inner circumferential surface of the stator 3a for rotatably supporting the shaft 2a, and a chucking mechanism 4 having an accommodating portion 4b accommodating therein the balance member 4a. Also, a disk mounting surface 4c is formed on an outer circumferential surface of the chucking mechanism 4 on which an optical disk (not shown in FIG. 7) is placed. Also, a plurality of aligning claws 4d are formed at a central portion of the chucking mechanism 4 wherein the aligning claws 4d make contact with an inner circumferential surface of a central opening portion of the optical disk in order to align the optical disk with a rotational center of the brushless motor 1. The plurality of the aligning claws 4d are arranged in a circumferential manner evenly apart from one another.
Currently due to lack of standardization for different types of high density optical disks (e.g., HD-DVD, Blu-ray), each type of optical disk requires a specific optical pickup mechanism. In order to use different types of optical disks each having a unique standard, at least two lenses arranged in a radial direction each emitting an optical disk will be needed for the optical pickup mechanism. By virtue of such configuration of the optical pickup mechanism, when one of the at least two lenses arranged further away from a brushless motor is at an area corresponding to, with respect to the optical disk, a radially innermost recordable/reproducible area of the disk, the other lens (i.e., nearer to the brushless motor) will be positioned furthermore inward of recordable/reproducible area of the disk.
However, the balance member 4a and the accommodating portion 4b of the chucking mechanism 4 in the brushless motor 1 are arranged such that they are axially overlapping with the disk mounting surface 4c. By such configuration, a pickup mechanism (not shown) for recording data on the optical disk and reproducing data from the optical disk will move further inward of the disk mounting surface 4c, and therefore, the accommodating portion 4b of the chucking mechanism 4 will interfere with the pickup mechanism. That is to say that the lens arranged further away from the brushless motor will not be able to record data on the optical disk or reproduce data from the optical disk at the recordable/reproducible inner most area of the disk.
Also, since optical disks are sometimes rotated at approximately 1,000 rpm while recording data on the disk and/or reproducing data from the disk, a slight unbalance in the rotation thereof may centrifugally affect the aligning claws 4d. Since the aligning claws 4 make contact with the central opening portion of the disk at a small portion thereof, the disk is not securely retained by the aligning claws 4. Therefore, when the disk is rotated at a very high speed and a centrifugal force becomes stronger than the force with which the aligning claws 4 retain the disk, a misalignment of the disk occurs which causes a vibration problem of the brushless motor.